Game of Thrones has a massive cast of capable actors, and even the King's Landing inferno at the end of Season 6 only managed to make a dent in the number of surviving characters. We can never count on everybody earning screentime in a given season. Luckily, we already have confirmation that an especially awesome character will be back in Season 7.
12-year old powerhouse actress Bella Ramsey was spotted back in costume for another round of Game of Thrones. She'ill reprise her role as Lady Lyanna Mormont when the show returns for Season 7 in 2017. Game of Thrones was her small screen debut, and she made an immediate impression on audiences everywhere in her very first appearance. When Jon Snow and Sansa Stark were traveling the North in search of allies against Ramsay Bolton, they stopped at Bear Island to recruit House Mormont.
The siblings (or cousins) were surprised to discover that Lyanna's youth didn't stop her from being a strong leader, and it quickly became clear that her support for House Stark did not automatically extend to a bastard named Snow and a lady married to a Bolton. If Ser Davos hadn't managed to persuade Lyanna, Jon may not have had any forces of House Mormont at his side in the Battle of the Bastards. Sure, Lyanna only gave them 62 men from Bear Island for battle, but it was a start, and her allegiance was ultimately more valuable than any fighters she might have mustered. Without Lyanna Mormont, Jon Snow would likely not have been crowned King of the North in the Season 6 finale.
Now that the show has outpaced the A Song of Ice and Fire source material, even those of us who know the books by heart can't say for sure what role Lyanna Mormont will play in Northern politics in Season 7. Considering that Lyanna is responsible for rousing the heads of the other Northern houses into naming Jon as king, Jon may want to appoint her as his royal speechwriter. He's certainly not going to be able to rule the North by himself, even if he is the most qualified to deal with the threat of the White Walkers. She may be a child and she may not be a fighter, but Lyanna proved herself as one of the fiercest Northerners of the show to date.
The inclusion of a girl leader in the middle of a sea of grizzled Northmen was a great twist, and Bella Ramsey managed to stand out and hold her own as Lyanna despite being surrounded by older and more experienced actors. Hopefully she'll be as fearless and formidable in Season 7 as she was in Season 6.